1. Field of the Invention
This invention relates to a process for preparing 2,2'-anhydrocytidine-5'-phosphate having an antitumor activity and, more particularly, it relates to a process for preparing 2,2'-anhydrocytidine-5'-phosphate in high yield via a novel intermediate 2',3'-0-sulfinyl-cytidine-5'-phosphate from cytidine-5'-phosphate. The present invention also relates to a novel intermediate, 2',3'-0-sulfinyl-cytidine-5'-phosphate represented by the formula (I) ##STR2## and a process for preparing 2',3'-0-sulfinyl-cytidine-5'-phosphate which comprises reacting cytidine-5'-phosphate with a thionyl halide in a polar organic solvent in the presence of a cyclic tertiary amine.
2. Description of the Prior Art
It is well known that 2,2'-anhydrocytidine-5'-phosphate per se possesses an antitumor activity as reported in Gann., 64, 519-522 (1973), Japan, and is also expected to have an anti-leukemia activity which is useful as a chemotherapy agent for treating and alleviating the leukemia.
Hitherto, various processes have been proposed for preparing 2,2'-anhydrocytidine-5'-phosphate such as a process comprising a specific phosphorylation of 2,2'-anhydrocytidine-5'-phosphate as proposed by the present inventors disclosed in Japanese patent application OPI No. 5997/1974, a process comprising heat-reacting cytidine-5'-phosphate in the presence of a large excess of a partially hydrolyzed phosphorus oxychloride in ethyl acetate as reported by T. Kanai et al., Tetrahedron Letters, 22, 1965-1968 (1971), etc. However, these prior art processes have serious disadvantages in that they require a large excess of phosphorus oxychloride which results in the formation of a large amount of undesirable inorganic acids and inorganic salts as by-products and that 2,2'-anhydrocytidine-5'-phosphate is easily decomposed into (1-.beta.-D-arabinofuranosyl)cytidine-5'-phosphate since 2,2'-anhydrocytidine-5'-phosphate is extremely unstable under alkaline conditions, and thus the above conventional processes necessitate markedly complicated and cumbersome procedures in purifying and isolating the desired product and also a large amount of expensive reagents.
For the above reasons, these conventional processes are not considered to be appropriate for the production of 2,2'-anhydrocytidine-5'-phosphate on an industrial scale.